This invention relates to a cylinder head gasket for an internal combustion engine equipped with a precombustion chamber built into the cylinder head. One part of the bottom wall of the precombustion chamber block is in engagement with the cylinder head gasket.
For achieving a more thorough admixing and thus a better combustion of the fuel/air mixture, it is known to provide--particularly diesel engines--with a precombustion chamber, side chamber, turbulence chamber or Ricardo-chamber arranged upstream of the main combustion chamber. The walls constituting the block in which such auxiliary chambers are defined must be made of materials resisting high temperatures, such as metals or sintered ceramic, preferably sintered silicon nitride. The block is received in an appropriate cavity of the cylinder head as a separate structural component. The installed precombustion chamber block engages the cylinder head gasket with one part of its bottom face so that the precombustion chamber block is prevented from dropping out of the cylinder head and further, there is ensured a sealing of the main combustion chamber.
During engine operation, significant heat generation occurs in the precombustion chamber and the bottom face of the precombustion chamber block is thus heated to high temperatures. The cylinder head gasket must therefore be protected in a particular manner in the zone of engagement with the precombustion chamber block.
According to German Patent No. 2,856,186 the legs of the sheet metal armor which frames each gasket opening aligned with a respective main combustion chamber of the engine are extended in a tab-like manner in the zone of the precombustion chamber block.
According to German Patent No. 3,011,216 each gasket opening associated with a combustion chamber has a bay-like enlargement, as a result of which the precombustion chamber block engages the metallic frame of the cylinder head gasket only with an external, less heated edge zone.
According to U.S. Pat. Nos. 4,311,318 and 4,400,000 each gasket opening associated with a combustion chamber is surrounded by a metallic fire ring which is secured to the cylinder head gasket by means of a frame. In the zone of the bottom of the precombustion chamber block a recess or cutout is provided in the cylinder head gasket so that the precombustion chamber block engages with the bottom face the fire ring and the cylinder head gasket only along an edge zone of the chamber block bottom.
An appropriate sealing of the precombustion chambers, however, involves many difficulties. Thus, the significantly heated precombustion chamber walls which engage the tab-like extended legs of the gasket armor may impart excessive stresses thereto because of the thermal expansion forces, resulting in a reduction of the sealing pressure which may cause gas leakages. Particularly in case the precombustion chambers are made of up-to-date ceramic materials, a proper sealing is even more difficult to achieve because of the significantly higher temperatures as compared to those present in metallic precombustion chambers
Further, ceramic precombustion chamber blocks are relatively brittle and breakable. In case of excessive sealing pressures, risks are high that the chambers break and therefore the prevailing sealing pressures must be unusually low.
Further, it is a disadvantage of bay-like enlargements in gasket openings that they constitute harmful free spaces facing the respective combustion chamber.